Radial pneumatic light truck or automobile tire

ABSTRACT

A radial ply pneumatic tire  30  has a unique cross sectional profile. The tires rum flange width W is greater than the tread width TW and the maximum section width SW is located radially less than 50% of the section height SH as measured from the nominal rim diameter ND.

TECHNICAL FIELD

This invention relates to a radial ply pneumatic tire, more specificallyto an improved cross section profile for such tires.

BACKGROUND ART

Subtle changes in the molded shape of a pneumatic radial tire, thematerials used to make the tire, the design of the tread pattern or thebelt package or the reinforcing members can improve or detract from theperformance of the tire. The tire designer is under constant pressure toimprove the overall performance of the tire. In his pursuit of improvingthe product, he often must reverse or abandon the previously conceiveddesign approaches and start anew with previously considered unworkabledesigns or approaches which when creatively applied in a new way solveproblems or achieve performance goals heretofore believed unachievable.

Pneumatic tires are one of the most complex laminated compositestructures devised by man. They are inherently difficult to correctlymodel and are routinely simplified in analysis leading to clearlyerroneous design theories and approaches.

The very nature of the tire makes it possible for many conflictingdesign approaches to survive and even flourish because the structure isso complex that multiple variables are constantly being adjusted tooptimize a particular design theory.

One particularly important variable that influences a tires performanceis its molded shape and its resultant cross sectional profile when thetire is mounted and inflated on its design rim.

Rhyne et al in U.S. Pat. No. 5,637,162 assigned to Michelin teaches atire structure for Improved Tread Life that claims a particular carcassand belt profile when the tire is properly inflated. The profile has asmaller than normal outside diameter combined with a largercross-sectional width which enables a tread to have a flatter widertread arc width which reduced the contact pressure across the treadprofile. The resultant profile enables the tread life to achieve about100,000 miles of service. Its tread width as taught extends axiallyoutwardly of the mounted bead width.

An earlier U.S. Pat. No. 4,669,519 issued Jun. 1, 1987 to Tagaski et al,teaches a Reduced Rolling Resistance Pneumatic Radial Tire which has amolded lower sidewall and bead area that is 20%-50% wider than itsdesign rim width. The tires profile is such that the maximum sectionwidth is located radially in the upper sidewall region or greater than50% of the tires section height as measured from the nominal rimdiameter. The conventional radial tire has the maximum section widthlocated at a radial height about 50% of the section height. ThisBridgestone Patent teaches that the hysterectic shear stresses in theshoulder region of the sidewall generates the most losses in terms ofrolling resistance and that by minimizing these losses a benefit inreduced rolling resistance can be achieved because the tread shoulderswill run cooler.

Both of these diverging solutions are plausibly correct. That is thebeauty of the tire art. The engineers can practice what appears to becontradicting approaches to get to a similar improved result. It is forthat reason that so many patents are issued. The unexpected resultsabound. Those of ordinary skill in the tire art routinely teach awayfrom particular ideas, which are latter, discovered to providebeneficial solutions.

The prior art Patent No. GB-A-2 224703 assigned to Sumitomo Rubber Ind.,Ltd. is regarded as the most relevant prior art and it teaches thefeatures found in the preamble of claim 1; wherein the maximum sectionwidth of the tire is greater than the rim flange width and the treadwidth is less than the rim flange width.

The subject matter of the present invention teaches a novel tire profilethat appears to be contrary to both of the above prior art patents andanother departure from the conventional wisdom of those of ordinaryskill in the art.

An object of the present invention is to provide a tire profile thatminimized the rolling resistance of tire while minimizing the effect ofthe tread compound selection. In other words desensitizing the tiresrolling resistance performance as a function of tread compounding.

Another object of the invention is to provide a lightweight tire.

Another object of the invention is to improve treadwear service mileage.

These and other objectives have been demonstrated by the tire asdescribed here below.

SUMMARY OF THE INVENTION

A radial ply pneumatic tire is disclosed. The tire 30 has a maximumsection width SW, a maximum section height SH, the ratio of SH/SWdefining the tire aspect ratio, the aspect ratio being 85% or less. Thetire has a nominal rim diameter ND, a nominal rim flange width W, and atread having a tread width, TW.

The tire 30 has the maximum section width SW being located within aradial distance X from the nominal rim diameter ND, the distance X beingless than a 50% of the maximum section height SH and wherein the maximumsection width SW is greater than the rim flange width W and the treadwidth TW is less than the rim flange width W.

Preferably the distance X is about 40% of the maximum section height SH.The maximum section width SW is preferably at least 10% greater than thenominal rim flange width W and the tread width is preferably a least 10%less than de nominal rim flange width W.

The tire 30 his a carcass structure 36 having one or more radial ply,the ply or plies extended to and at least one ply is wrapped about orotherwise attached to a pair of annular bead cores 35. The radial pliesare reinforced by parallel cords 20. The tire 30 when mounted on itsdesign rim 40 and inflated has the cords 20 placed in tension. At alocation between the radial location of the maximum section width SW andthe nominal rim diameter ND a line L₁, drawn through a point Y, thepoint Y intersecting the bead at the location of the nominal rimdiameter ND, and tangent to the sidewall 21 is inclined radially andaxially inwardly at an angle θ relative to the rim flange, θ being lessthan 40° in each sidewall 21.

The tire 30 has its sidewall 21, at a radial location Z between thelocation of the maximum section width SW and the radially outmostsection height location SH, inclined such that a line L₂ drawn through Zand tangent to the sidewall 21 radially inwardly and axially outwardlyis inclined at an angle β, relative to a plane perpendicular to thetires aids, θ being 90% of β or greater in each sidewall 21. Preferablyθ is about equal to β, most preferably in the range of 90-120% of β.

The locations Y and Z he on an axis A passing through the centroid C ofthe sidewall, the axis A being perpendicular to the tire axis ofrotation. The centroid C of each sidewall is defined by the area withinthe sidewall 21 and between a line 70 drawn through a tread edge 30A or30B and a tangent to the axially inner portion of the bead area 33 atlocation 12.

Definitions

“Aspect ratio” of the tire means the ratio of its section height (SH) toits section width (SW) multiplied by 100% for expression as apercentage.

“Axial” and “axially” means lines or directions that are parallel to theaxis of rotation of the tire.

“Bead” means that part of the tire comprising an annular tensile memberwrapped by ply cords and shaped, with or without other reinforcementelements such as flippers, chippers, apexes toe guards and chafers, tofit the design rim.

“Belt structure” or “Reinforcing Belts” means at least two annularlayers or plies of parallel cords, woven or unwove, underlying thetread, unanchored to the bead, and having both left and right cordangles in the range from 17 degrees to 27 degrees with respect to theequatorial plane of the tire.

“Carcass” means the tire structure apart from the belt structure, tread,undertread, and sidewall rubber over the plies, but including the beads.

“Circumferential” means lines or directions extending along theperimeter of the surface of the annular tread perpendicular to the axialdirection.

“Cord” means one of the reinforcement strands of which the plies in thetire are comprised.

“Design rim” means a rim having a specified configuration and width. Forthe purposes of this specification, the design rim and design rim widthsare as specified by the industry standards in effect in the location inwhich the tire is made. For example, in the United States, the designrims are as specified by the Tire and Rim Association. In Europe, therims are as specified in the European Tyre and Rim TechnicalOrganization—Standards Manual and the term design rim means the same isthe standard measurement rims. In Japan, the standard organization isThe Japan Automobile Tire Manufacturer's Association.

“Design rim width” means the specified distance axially between rimflanges. For the purpose of this specification, the design rim width (D)is taken as (the minimum recommended rim width plus the maximumrecommended rim width)/2 as specified by the appropriate industrystandards.

“Equatorial plane (EP)” means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

“Innerliner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire.

“Normal inflation pressure” refers to the specific design inflationpressure and load assigned by the appropriate standards organization forthe service condition for the tire.

“Normal load” refers to the specific design, inflation pressure and loadassigned by the appropriate standards organization for the servicecondition for the tire.

“Ply” means a continuous layer of rubber-coated parallel cords,

“Radial” and “radially” means directions radially toward or away fromthe axis of rotation of the tire.

“Radial-ply tire” means a belted or circumferentially-restrictedpneumatic fix in which the ply cords, which extend from bead to bead arelaid at cord angles between 65° and 90° with respect to the equatorialplane of the tire.

“Section height” (SH) means the radial distance from the nominal rimdiameter to the outer diameter of the tire at its equatorial plane.

“Section width” (SW) means the maximum linear distance parallel to theaxis of the tire and between the exterior of its sidewalls when andafter it has been inflated at normal pressure for 24 hours, but unloadedexcluding elevations of the sidewalls due to labeling, decoration orprotective bands.

“Sharp diameter” means the diameter as measured radially across the tirethrough the axis to the points defined by the intersection of a fineextending tangent the bead seat or first surface and a line extendingtangent the bead flange or second surface.

“Shoulder” means the upper portion of a sidewall just below the treadedge. Affects cornering.

“Sidewall” means that portion of a the between the tread and the bead.

“Tread width,” means the arc length of the tread surface in the axialdirection, that is, in a plane passing through the axis of rotation ofthe tire.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of the tire according to a preferredembodiment of the invention as shown mounted on its design rim.

FIG. 2 is an enlarged view of a sidewall portion of the tire of FIG. 1.

FIG. 3 is a schematic representation of the sidewall profile of FIG. 2.

FIG. 4 is a cross sectional view of a standard design rim.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is illustrated a cross sectional view of atire 30 made in accordance with the present invention. In the particularillustrated embodiment, the tire 30 is a low aspect ratio passengertire. As shown, the beads 33 are spaced axially a distance (W) equal tothe specified design rim width D.

The tire 30 is provided with a ground-engaging tread portion 31, whichterminates in the shoulder portions 32 at the lateral edges 30A and 30Bof the tread 31. Radially outer sidewall portion 21 extends fromshoulder portion 32 and terminates in the bead portion 33, the beadportion having an annular inextensible annular tensile member or beadcores 35. The tire 30 is further provided with a carcass reinforcingstructure 36 having one or more radial plies which extends from thetensile member 35 through the sidewall portion 21, the tread portion 31,the opposite sidewall portion 21 down to the opposite tensile member 35.At least one pair of turnup ends 38 of the carcass reinforcing structure36 are preferably wrapped about the tensile members 35. As illustrated,the bead portion 33 has a chipper 41 wrapped about the reinforcingmember 36 and tensile member 35. The tire 30 may include a conventionalinnerliner 37 forming the inner peripheral surface of the tire 30 if thetire is to be of the tubeless type.

Placed circumferentially about the radially outer surface of the carcassreinforcing structure 36, beneath the tread portion 31, is a treadreinforcing belt structure 39. In a preferred embodiment, the beltstructure 39 comprises two single cut belt plies and the cords of thebelt plies are oriented at an angle ranging between 17° and 25° withrespect to the equatorial plane of the tire. The cords of one belt plyare disposed in an opposite direction to the equatorial plane and fromthat of the cords of the other belt ply. However, the belt structure 39may comprise any number of belt plies of any desired configuration andthe cords may be disposed at any desired angle.

The carcass reinforcing structure 36 includes at least one reinforcingply structure comprising each one layer of parallel cords 20. The cords20 of the reinforcing ply structure 36 are oriented at an angle of atleast 75° with respect to the equatorial plane EP of the tire 30. Thecords 20 reinforcing the carcass ply 36 may be of any material normallyused for cord reinforcement of rubber articles, for example, and not byway of limitation, rayon, nylon, steel and polyester. The reinforcingply structure 36 has turnup ends 38, which wrap about the bead core 35,the ends being located at about 20% to 50% of the section height of thetire 30.

Before mounting the tire 30 on a rim 40 and inflating the tire 30 hasthe shape imparted to it by the mold. After mounting the tire 30 on therim 40, the inclination of the bead portions 33 of the tire 30 isimposed by the rim 40.

The bead 33 has a first annular surface 23 located between the bead toe22A and the bead heel 22B. The first annular surface is preferableinclined at an angle when the beads 33 are spaced a distance W. Thedistance W is equal to the design rim width D. For the purpose of thisspecification, the design rim width (D) is the average of the specifiedmaximum and minimum design rim widths, the widths being measured axiallybetween the rim flanges. The range of design rim widths is establishedby the industry standards applicable where the tire is made. In theUnited States, for example, the Tire and Rim Association standards haveestablished a range of recommended rim widths for “J” type rim in the14″ to 16″ rim diameter size, the range of widths for a 225/55R16 tirebeing 6.5 to 8.0 inches. The design rim width D as defined in theapplication, therefore, is 7.25 inches for the 225/55R16 tire. A tiremolded at a different bead width naturally may have different beadsurface orientations. However, when the beads are spaced a distance W asso defined, the orientation of the surfaces must fall within the rangeto achieve the benefits of the present invention.

Illustrated in FIG. 1 is a cross-sectional view of the tire 30 of thepresent invention. As shown the tire is mounted on its design rim 40 andis inflated but not loaded.

Each tire 30 has a specific recommended design rim 40 for eachparticular tire size. The design rim 40 as shown in FIG. 4 has a pair ofannular rim flanges 44 therein flanges restrain the axially growth ofthe bead area of the tire 30. The axial distance between the flangesdefines the rim width D. The bead seats 42 of the rim 40 are set at aslight taper B_(R) for passenger tires usually a 5° taper. Theintersectional of the rim flange 44 and the bead seat 42 of the of thedesign rim 40 define the tire nominal rim diameter ND. The rim flange 44is inclined at an angle _(αR) generally 0° to 2° off vertical. Theflange has an outer radius R_(R2) and an inner radius R_(R1) as shown.

The tire 30 as shown in FIG. 1 has a maximum section width SW, a maximumsection height SH, the ratio SH/SW defines the tire aspect ratio. Thisinventive tire has an aspect ratio, of 85% less. The tire 30 has anominal rim diameter ND, a nominal rim flange width W and a tread 31having a tread width TW.

As shown the maximum section width SW is located width a radial distanceX from the nominal rim diameter ND. The distance X is less than 50% ofthe maximum section height SH, preferably the location X is about 40% orless. The maximum section width SW is preferably at least 10% greaterthan the rim width W and the tread TW width is at least 10% less thanthe nominal rim flange width.

The above relationship of section height, section width, rim flangewidth are all established when the tire is inflated and mounted on itsdesign rim, but unloaded. As previously stated, the tire 30 of thepresented invention is preferably molded at a different bead width. Therecommended molded bead width is preferably about 1 inch (2.5 cm)greater than the design rim width D of about 7.25 inches (18.4 cm) forthe exemplary 225/55R16 tire size or generally about 15% greater thanthe design rim width.

Thus when the tire 30 is mounted to its design rim 40 the beads 33 aremoved closer together than the tires molded bead width. This causes theply cords 20 to be slightly pre-loaded or tensioned. This is believed toenhance the responsiveness of the tire 30 in terms of handlingperformance.

This is particularly significant because the inflated tires profile is aradical departure from the radial ply tires of the prior art.

The tire 30 has a relatively flat tread 31 with the entire tread lyingbetween and axially narrower than the tires design rim width D, thetread width TW being measured between the tires lateral edges 30A, 30B.This narrowing of tread width TW commonly is considered to decreasetread mileage. This need not be the case, however, because the uniquetire profile actually increases the tread unit pressure slightly becauseof the reduced footprint area. This increased pressure is particularlybeneficial to the tread 31 adjacent the shoulder region 32 of the tire30. This in turn enables the tread 31 to wear more uniformly andaccordingly lasts longer.

The inventors found that the tire profile can permit a shallowernon-skid depth 50 of the tread 30 to be used. This also reduceshysterisis effects. Furthermore, because the tread shoulder regions 32,which is normally prone to high beat build-up, is narrowed further gainsin rolling resistance reductions can be achieved. All of thesebeneficial factors mean that the tire engineer can use tread compoundsthat wear better and have good traction properties without the normallyassociated loss in rolling resistance performance.

The tire 30 as further shown in FIG. 2 has a unique sidewall profile.The curvature is such that the sidewall 21 acts like a curved beambetween the lateral tread edge 30A or 30B at location 10 and the axiallyinner surface of the ply adjacent the bead core at location 12.

If one uses the inflated but unloaded sidewall path and a straight line70 drawn through points 10 and 12 a schematic representation of theprofile arm can be shown as in FIG. 3. Mathematically the centroid ofthis area can be located as a point in space indicated as C. Normallythe location C would be located at a radial location of 50% of thesection height SH as measured from the nominal rim diameter ND. The tire30 of the present invention has the centroid C well below 50% of thesection height SH, similarly the radial location of the maximum sectionwidth SW is below the 50% location of the section height SH.

If one draws a major axis A through this location C, the radially outerintersection of the axis A and the sidewall 21 is located at a Z, andthe radially inner intersection is located at Y. A line L₁ drawnintersecting Y and tangent to the sidewall is inclined radially andaxially outwardly at an angle θ relative to the centroid major axis A.

Complementing this, angular relationship the tangent line L₂ at locationZ is inclined at an angle β relative to the axis A, β being less than40° in each sidewall. The angle θ is 90% of β or greater in eachsidewall 21.

A test tire in a size P225/70R16 was evaluated using the above describedprofile and were compared against a production prior art Eagle LS tireof a similar size. Although not mandatory, the lateral extremes of thebelt reinforcing structure 39 should be located in close proximity tothe line 70 which passes through location 10 and 12. The test tire 30had an angle of θ of 32°, an angle β of 30° when mounted on a rim havinga 6.5 inches design rim flange width D, and a tread width TW of 5.9inches. The maximum section height SH was 5.75 inches and the radiallocation X of maximum section width SW was 2.55 inches as measured fromthe nominal rim diameter. The ratio of X/SH was 40.7%. The ratio of C/SHwas slightly more at 41.7%. The control tire had the tread width TWbeing 7.0 inches which is wider than the rim flange width, the angle βwas 22°, while θ was 36° using the mine size rim 40, with X being 43%.The belt structure 39 location of the lateral extremes of the inventivetire 30 can be on either side of the line 70, preferably on line 70. Thetest tire has improved ride and handling, a slightly better wet handlingperformance compared to the control tire. Most significantly, a greaterthan 1 Kg. reduction in weight was achieved compared to the controltire.

Similar improvements were noted in a tire size P185/70R14. The results,of this testing confirmed that a lighter weight lower cost tire could bemade using the novel profile while at the same time improving the tiresoverall performance.

An alternative method of approximating the upper and lower sidewallangles θ and β is to take a tangency to the sidewall 21 of the tire 30at a radial location of 75% SH and 25% SH, at these two locations theangles θ and β are approximately the same as if measured as suggested atthe locations, as defined previously.

What is claimed is:
 1. A radial ply passenger or light truck pneumaticthe having an axis of rotation, a maximum section width SW, a maximumsection height SH, the maximum section height SH/the maximum sectionwidth SW defines the tires aspect ratio, the aspect ratio being 85% orless, a nominal rim diameter ND, a nominal rim flange width W, and atread having a pair of tread edges defining a tread width TW, themaximum section width SW being located at a radial distance X from thenominal rim diameter ND, the distance X being less than 50% of themaximum section height SH and wherein the maximum section width SW isgreater than the rim flange width W and the tread width TW is less thanthe rim flange width W, a pair of sidewalls, each sidewall having acentroid C, the centroid C being defined by the area within the sidewalland between a line drawn through a first or second tread edge andtangent to an axially inner portion of a bead adjacent to a bead core,the centroid C having a major axis A perpendicular to the tires axis ofrotation, the intersections of the axis A being Y at a radially innerintersection and Z at a radially outer intersection, the intersection Zof the axis A and the tire occurs at the sidewall characterized in thatthe intersection Y of the axis A and the tire occurs in the bead portionat the location of the nominal rim diameter ND; whereby the centroid Cis located at a radial location greater than the radial location X ofthe maximum section width SW but less than 50% of the section height SH.2. The tire of claim 1 wherein the distance X is 40% or less of themaximum section height SH.
 3. The tire of claim 1 wherein the maximumsection width SW is at least 10% greater than the rim flange width W. 4.The tire of claim 1 wherein the maximum tread width TW is at least 10%less than the rim width W.
 5. The tire of claim 1 further characterizedby one or more radial ply, the radial ply or plies extending to a pairof annular bead cores at least one ply being wrapped about or otherwiseattached to the bead cores, the radial plies being reinforced by cords,the tire when mounted on a design rim and inflated and unloaded has thecords placed in tension, and at the location Y, a line L₁ drawnintersecting Y and tangent to the sidewall is inclined radially andaxially outwardly at an acute angle θ relative to the major axis A, θbeing less than 40° in each sidewall.
 6. The tire of claim 5 wherein thesidewall at a radial location Z midway between the location of themaximum section width SW and the radially outermost section heightlocation SH, a line L₂ drawn intersection Z and tangent to the sidewallis inclined at an angle β radially inwardly and axially outwardlyrelative to the axis A, θ being 90% of β or greater in each sidewall.